Nonwoven fabric made of core/sheath composite fiber and process for producing the same

ABSTRACT

A nonwoven fabric is comprised of sheath-core type bicomponent continuous fibers. The core portion is consisted of a polyester and the sheath portion is consisted of a polyethylene. The polyethylene may be a mixture of the first polyethylene polymerized by metallocene catalyst and the second polyethylene polymerized by Ziegler-Natta catalyst. The configuration of the cross section of the core portion do not change along the axial direction. The core portion has the substantially same diameter. On the other, the thickness of the sheath portion is changed irregularly and at random along the axial direction and circular direction of the fiber. That is, the surface of the sheath portion is irregular unevenness. Therefore, the nonwoven fabric containning the bicomponent fibers is very soft. The nonwoven fabric may be obtained by accumulating the fibers which are melt spun out sheath-core type spinning holes. The polyester is provided to each core hole, and the polyethylene is provided to each sheath hole of the spinning holes.

TECHNICAL FIELD

The present invention relates to a nonwoven fabric which is comprised ofspecific sheath-core type bicomponent fibers. And the nonwoven fabrichas an excellent property into softness and adhesion by heating.Furthermore, the invention relates to a method of the nonwoven fabric.

BACKGROUND ART

A nonwoven fabric is known which is composed of sheath-core typebicomponent fibers. Especially, it is known that a nonwoven fabric iscomposed of sheath-core type bicomponent continuous fibers each of whichis consisted of a sheath portion made of polyethylene and a core portionmade of polyester, and the nonwoven fabric is used as a heat sensitiveadhesive nonwoven fabric (JP 8-14069 B, claim 1 in page 1).

The heat sensitive adhesive nonwoven fabric is laminated to an othermaterial etc., and is heated and if necessarily pressed. Then, the heatsensitive adhesive nonwoven fabric is adhered to the other materials bymelting or softening the polyethylene only of the sheath portion,because the heat sensitive adhesive nonwoven fabric is composed of thesheath-core type bicomponent continuous fibers each of which isconsisted of the sheath portion made of the polyethylene having lowmelting point and the core portion made of the polyester having highmelting point.

SUMMARY OF THE INVENTION

The inventor has investigated to lower the melting point of thepolyethylene in order to improve adhesive property of the heat sensitiveadhesive nonwoven fabric. In this investigation, using a specificpolyethylene instead of the conventional polyethylene, the inventor hasdiscovered that a specific sheath-core type bicomponent continuous fiberis obtained which is distinguished from the above said conventionalsheath-core type bicomponent continuous fiber. That is, the inventor hasdiscovered that the surface of specific bicomponent continuous fiber isirregularly uneven. The inventor has further discovered that thespecific bicomponent continuous fiber has not a constant diameter, thatis, has thin diameter parts and thick diameter parts, therefore thefiber is very soft because of the thin diameter parts. Accordingly, thenonwoven fabric consisted of the specific bicomponent continuous fibersis very soft.

The object of the invention is to provide a very soft nonwoven fabricbased on the above discovery.

The invention relates to the nonwoven fabric containing specificsheath-core type bicomponent fibers. The sheath portion of thebicomponent fiber is formed by polyethylene, and the thickness of thesheath portion is changed irregularly and at random along the axialdirection and circular direction of the fiber. The core portion of thebicomponent fiber is formed by polyester, and the configuration of thecore portion is not substantially changed along the axial direction ofthe fiber.

DESCRIPTION OF THE INVENTION

The nonwoven fabric is containing the specific sheath-core typebicomponent fibers. The sheath-core type bicomponent fiber may be astaple fiber or a continuous fiber (filament). The continuous fiber maybe suitable because of generally using a spunbond process to obtain thenonwoven fabric of the invention. The sheath-core type bicomponent fiberis consisted of the sheath portion made of polyethylene and the coreportion made of polyester. Since the solubility of the polyethylene andthe polyester is moderately poor, the specific sheath-core typebicomponent fiber may be obtained. If the core portion is formed bypolypropylene which has good solubility to polyethylene, it is difficultto obtain the specific sheath-core type bicomponent fiber. And if thecore portion is formed by polyamide which has very poor solubility topolyethylene, it is too difficult to obtain the specific sheath-coretype bicomponent fiber.

The configuration in cross section of the core portion is notsubstantially changed along the axial direction of the fiber as same asthe prior arts. Typically, the configuration in cross section of thecore portion may be a circle, and the diameter of the circle is notsubstantially changed along the axial direction of the fiber. Thepolyester forming the core portion may be polyethylene-terephthalatemarketed or used industrially, especially marketed or used on textileindustry. Concretely, it is suitable to use polyethylene-terephthalateof which the limiting viscosity is 0.50-1.20.

The surface of the specific sheath-core type bicomponent fiber, that is,the surface of the sheath portion is irregularly uneven. The irregularunevenness comes out because the thickness of the sheath portion changesunequally and at random along the axial direction and circular directionof the fiber. The thickness of the sheath portion is zero in a partwhich is not having the sheath portion, that is, in the part which thecore portion is exposing. When the diameter of the core portion is φ₀,and the diameter of the bicomponent fiber in the part having most thicksheath portion is φ₁, the diameter of the bicomponent fiber changes atrandom in the range of φ₀˜φ₁ along the axial direction of thebicomponent fiber. Concurrently, the radius of the core portion is φ₀/2,and the radius of the bicomponent fiber in the part having most thicksheath portion is φ₁/2, the radius of the bicomponent fiber changes atrandom in the range of φ₀/2˜φ₁/2 along the circular direction of thebicomponent fiber. However it is described in the above case that theconfiguration of the cross section of the core portion and thebicomponent fiber is circle, the configuration may be not circle. In thecase the configuration is not circle, the diameter or the radius means adiameter or a radius of imaginary circle corresponding to cross sectionarea of the bicomponent fiber.

It is suitable to use a mixture of a first polyethylene having highspinnability and a second polyethylene having low spinnability as thepolyethylene forming the sheath portion. When using only the firstpolyethylene having high spinnability, it is difficult to come outirregular unevenness. That is, the bicomponent fiber may be same as thatof the prior art. On the other hand, using only the second polyethylenehaving low spinnability, it is difficult to obtain the bicomponent fiberby the process of melt spinning. It is suitable to mix 30-70 weight % ofthe first polyethylene and 70-30 weight % of the second polyethylene. Asthe first polyethylene, it is most suitable to use the polyethylenepolymerized by metallocene catalyst. Because, the polyethylenepolymerized by metallocene catalyst has low melting point and highspinnability. As the second polyethylene, it is common to use thepolyethylene polymerized by Ziegler-Natta catalyst, that is, soldindustrially. It is most suitable to use the low density polyethylenewhich has low melting point and low spinnability. The low densitypolyethylene may be 0.910-0.925 g/cc of density.

It is suitable that the weight mass of the sheath portion is 20-300weight mass per 100 weight mass of the core portion. The weight ratiomeans an average, because the thickness of the sheath portion ischanging irregularly or at random along the axial direction and circulardirection of the fiber. If the weight mass of the sheath portion islower than 20 weight mass, it is difficult to obtain high adhesivestrength, in the case of using the sheath portion as an adhesive agent.If the weight mass of the sheath portion is higher than 300 weight mass,the weight mass of the core portion is relatively smaller. Accordingly,because the diameter of the core portion becomes fine, the tensilestrength is lower in the part which the core portion is exposing, thatis, the sheath portion is not existing.

It is suitable that a fineness of the specific sheath-core typebicomponent fiber is 1.0-10 dtex. The fineness means an average becausea fineness changes irregularly or at random along the axial direction ofthe fiber.

The forms of the specific sheath-core type bicomponent fibers are shownin the FIG. 1-3. An inside between two parallel straight lines expressesthe core portion. As shown, the diameter of the core portion does notsubstantially change. The sheath portion is expressed by surges whichare existing on the upper and the lower of the two parallel straightlines. As clearly shown, the thickness of the sheath portion changesirregularly or at random along the axial direction and circulardirection of the fiber. FIG. 8 shows each concrete configuration ofcross sections of the bicomponent fibers. It may be understood that thethickness of the sheath portion changes irregularly or at random alongthe circular direction of the fiber.

A weight of the nonwoven fabric containing the specific sheath-core typebicomponent fibers is not restricted, but it is suitable that the weightis 10-100 g/m². When two pieces of the nonwoven fabric are laminated andthe edges are adhered by heating, it is possible to obtain a bag.Furthermore, when the nonwoven fabric is laminated with a plastic film,a woven or knitted fabric, a paper, or an other nonwoven fabric andadhered by heat-sealing, it is possible to obtain a composite material.That is, when the heat and if necessarily press is given to thepolyethylene forming the sheath portion, the two pieces of the nonwovenfabric are adhered or the nonwoven fabric is adhered to the othermaterial by the melting or softening polyethylene. Especially, in thecase that the polyethylene forming the sheath portion is the mixture ofthe first polyethylene polymerized by metallocene catalyst and thesecond polyethylene which is low density polyethylene, it is possible toadhere by heating on lower temperature, because the polyethylene formingthe sheath portion has lower melting point. Furthermore, if the othermaterial is the material made of polypropylene, especially polypropylenefilm, it is possible to obtain a composite material of which thenonwoven fabric and the material are strongly adhered, because thepolyethylene forming the sheath portion has good solubility topolypropylene. In the case that the other material is a polyethylenefilm, it is advantage that the polyethylene film is hardly shrunk,strained and transformed by heating.

A typical method of the nonwoven fabric relating to the invention iscomprised of the following steps. The polyester and the polyethylene areprepared. The polyethylene is the mixture of the first polyethylenepolymerized by metallocene catalyst and the second polyethylenepolymerized by Ziegler-Natta catalyst. The polyester is provided to eachcore hole of sheath-core type spinning holes. The polyethylene isprovided to each sheath hole of the above said spinning holes. By usingthe above said sheath-core type spinning holes, the polyester and thepolyethylene are spinning together, and the specific sheath-core typebicomponent continuous fibers are obtained. The nonwoven fabric relatingto the invention is obtained by accumulating the bicomponent continuousfibers.

As the polyester, the first polyethylene polymerized by metallocenecatalyst and the second polyethylene polymerized by Ziegler-Nattacatalyst, what were above described are used. The first polyethylene andthe second polyethylene are mixed at the above described ratio ofweight, and the mixture is used as the polyethylene.

It is suitable that the melt flow rate (MFR) of the polyethylene is16-21 grams per 10 minutes. In this range, it is easy to form the sheathportion of which the surface is irregular unevenness when spinning at ahigh speed. However, it is possible to form the sheath portion of whichthe surface is irregular unevenness, by spinning at a higher speed whenthe value of MFR is larger than the above range, or by spinning at alower speed when the value of MFR is smaller than the above range. It issuitable that the value of MFR is in the above range, when spinning at3000-4000 meters per a minute which is commonly used. It is suitablethat the melting point of the polyethylene is lower, especially is90-110° C. Because it is possible to adhere by heating in a lowtemperature.

The polyethylene and the polyester are heated and molten. The moltenpolyester is provided to each core hole of the sheath-core type spinningholes in a spinneret. The molten polyethylene is provided to each sheathhole of the above spinning holes. By melt spinning the polyester and thepolyethylene, it is possible to obtain the sheath-core type bicomponentcontinuous fibers of each of which the surface is irregular unevenness.The invention is characterized by being able to stably obtain thesheath-core type bicomponent continuous fiber of which the surface isirregular unevenness, that is, the diameters of the bicomponent fiberdiffer in the axial direction of the fiber. On the melt spinning in theprior art, the continuous fiber of which the diameters differed did notbe obtained, because the continuous fiber cuts at fine diameter parts.That is, on the conventional melt spinning, in the case that anunevenness is formed on the surface of the fiber, the unevenness isformed just after the melt spinning when the resin as polyester etc. hashigh fluidity. Because the stress at the melt spinning is centralized inparts of fine diameters for the high fluidity, the spinning fiber iseasy to cut in the parts of the fine diameters. Accordingly, thecontinuous fiber of which the surface is irregular unevenness may not bestably obtained. However, the continuous fiber may be stably obtained bythe invention. The principle of the invention may be as the following.That is, using mixture of the first polyethylene and the secondpolyethylene, the unevenness is not formed just after the melt spinningwhen the resin as polyester etc. has high fluidity. On the time whichthe core portion is solidified or after the time, the irregularunevenness may be formed because the polyethylene of the sheath portionis stressed. The reason of the stress of the polyethylene is that thepolyethylene is the mixture of the first polyethylene having highspinnability and the second polyethylene having low spinnability. Thatis, the first polyethylene may form the fiber with the polyester, butthe second polyethylene may obstruct to form the fiber.

After the sheath-core type bicomponent continuous fibers are obtained,the fibers are accumulated on the moving conveyor. A web formed byaccumulating the fibers is partially heated and pressed by passingthrough between a pair of embossing rolls etc. The sheath portions aremolten or softened at the parts which the heat and press are given. Thebicomponent fibers are bonded at the parts with each other. And it ispossible to obtain the nonwoven fabric which has high tensile strength.The nonwoven fabric comprised of the sheath-core type bicomponent fibersis suitably used to obtain the composite material adhering the nonwovenfabric to the other materials by heating as the above described.Furthermore, the nonwoven fabric is suitably used to obtain the bag ofwhich the edges are adhered by heating as the above described. Thenonwoven fabric is used as a material of a garment, of a sanitary, of aindustry, of an agriculture and of a living.

The nonwoven fabric relating to the invention is comprised of thesheath-core type bicomponent fibers. The fiber is consisted of the coreportion of which the configulation in cross-section is not substantiallychanged along the axial direction of the fiber and the sheath portion ofwhich the thickness is changed irregularly and at random along the axialdirection and circular direction of the fiber. That is, the fiber hasparts of fine diameters and parts of thick diameters along the axialdirection of the fiber. Softness is given to the fiber because the partsof fine diameters exist. Tensile strength of the fiber is same as asheath-core type bicomponent fiber in the prior art, because thediameter of the core portion is not changed along the axial direction ofthe fiber. Accordingly, the nonwoven fabric comprised of the above saidbicomponenet fibers has two properties which are the softness and thehigh tensile strength.

The sheath-core type bicomponent fiber diffusely reflects visible ray,because the surface of the fiber is irregularly unevenness.

Accordingly, the nonwoven fabric comprised of the fibers may be whitish.

In the case that the polyethylene of the sheath portion is the mixtureof the first polyethylene and the specific second polyethylene, thenonwoven fabric may be adhered to other material (included nonwovenfabric) by heating on low temperature. Because the first polyethylenepolymerized by metallocene catalyst has low melting point, and, thespecific second polyethylene is low density polyethylene which ispolymerized by Ziegler-Natta catalyst and has low melting point.

In the method relating to the invention, the sheath portion is formed bythe mixture of the first polyethylene having high spinnability and thesecond polyethylene having low spinnability. When melt spinning thispolyethylene, the thick of the sheath portion becomes thickly and thinlyat random by the existing of the second polyethylene having lowspinnability. On the other hand, the core portion is formed of thepolyester, and the diameter of the core portion does not substantiallychange as the prior art. Accordingly, the sheath-core type bicomponentfiber of the core portion of which the configuration in cross-section isnot substantially changed along the axial direction of the fiber, and ofthe sheath portion of which the thickness is changed irregularly and atrandom along the axial direction and the circular direction of the fiberis stably obtained. And the nonwoven fabric comprised of the abovefibers is too stably obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view (micrograph) showing an example of a sheath-coretype bicomponent fiber relating to the invention.

FIG. 2 is a side view (micrograph) showing another example of asheath-core type bicomponent fiber relating to the invention.

FIG. 3 is a side view (micrograph) showing a further example of asheath-core type bicomponent fiber relating to the invention.

FIG. 4 is an enlarged view (micrograph) showing a surface of a nonwovenfabric obtained by a method of the following example 2.

FIG. 5 is an enlarged view (micrograph) showing a surface of a nonwovenfabric obtained by a method of the following example 3.

FIG. 6 is an enlarged view (micrograph) showing a surface of a nonwovenfabric obtained by a method of the following example 4.

FIG. 7 is an enlarged view (micrograph) showing a surface of a nonwovenfabric obtained by a method of the following example 5.

FIG. 8 is a cross sectional view (micrograph) showing an example of asheath-core type bicomponent fiber relating to the invention.

EXAMPLE

The invention is more described on examples as the followings, but theinvention is not limited in the range of the examples. The invention maybe understood on the discovery that it is stably able to obtain thesheath-core type bicomponent fiber of which the surface (that is, thesurface of the sheath portion) has irregular unevenness.

The values or properties in the examples were measured or evaluated asthe followings.

(1) Intrinsic Viscosity [η] of the polyester; It was measured bydissolving 0.5 gram of a sample in 100 cc of the solvent which was amixture of an equal parts of a phenol and an ethane tetrachloride on thecondition with 20° C.

(2) Melting Point [° C. ]; It was measured by using the differentialscanning calorimeter DSC-7 provided from PerkinElmer Inc. on thecondition that a speed rate of elevating temperature was 20° C. per aminute.

(3) Melt Flow Rate (g/10 minutes) of the polyethylene; It was measuredby a described method on JIS K 6922 on the conditions with 21.18N of aload and 190° C. of a temperature.

(4) Softness (g) of the nonwoven fabric; It was measured by a method ofa Handle-O-Meter which was in E method of an article of softness on JISL 1096.

(5) Soft feeling of the nonwoven fabric; It was evaluated by eachfeeling of each hand of 5 panelers. Nonwoven fabrics of the examples andthe comparative example were relatively evaluated into the followingranks.

1: It was soft.

2: It was a little soft.

3: It was not soft.

(6) Smoothness feeling of the nonwoven fabric; It was evaluated by eachfeeling of each hand of 5 panelers. Nonwoven fabrics of the examples andthe comparative example were relatively evaluated into the followingranks.

Good: It had a very smoothness.

Mid.: It had a smoothness.

Bad: It had little or no smoothness.

(7) Tensile Strength (N/5 cm in width) of the nonwoven fabric; It wasmeasured on JIS L 1096. That was, ten test strips of 50 mm in width and200 mm in length were prepared. Each test strip was tensioned by usingTensilon RTM-500 provided by Toyo Baldwin on the conditions of 100 mm indistance between chucks and 100 mm/minute in tensile speed. And averagetensile strength of ten test strips was the tensile strength. Thetensile strengths in MD direction (machine direction) and in CDdirection (cross direction to MD direction) were measured.

(8) Adhesion Strength (N) of the nonwoven fabric; Two test strips of 30mm (CD direction) and 150 mm (MD direction) were laminated. The partwhich was 50 mm from the edge of length direction (MD direction) wasadhered by heating in Heat Seal Tester. The adhesion by heating wascarried out at three kinds of temperature which was set up 100° C., 110°C. and 130° C. on the die. Furthermore the pressure was set up 98 N/cm²,and the area of the adhesion was set up 10 mm (MD direction) and 30 mm(CD direction).

The adhesion strength was measured on the method of T type peeling inJIS L 1089. That was, each of five test adhesive samples was tensionedby Tensilon RTM-500 provided by Toyo Baldwin on the conditions of 10 mmin distance between chucks and 100 mm/minute in tensile speed. Anadhesion strength was a strength when the sample was broken. And averageadhesion strength of five samples was the adhesion strength.

EXAMPLE 1

The polyethylene-terephthalate which was 0.70 in intrinsic viscosity [η]and 260° C. in melting point was prepared. On the other hand, thepolyethylene which was 18 g/10 minutes in melt flow rate, 0.911 g/cc indensity and 104° C. in melting point was prepared. This polyethylene wasthe mixture of the first polyethylene 60 weight mass and the secondpolyethylene 40 weight mass. The first polyethylene was polymerized bymetallocene catalyst and was 28 g/10 minutes in melt flow rate, 0.906g/cc in density and 97° C. in melting point. The second polyethylene waspolymerized by Ziegler-Natta catalyst and was 4 g/10 minutes in meltflow rate, 0.918 g/cc in density and 106° C. in melting point.

The polyester was provided to each core hole of the sheath-core typespinning holes and the polyethylene of which the weight was equal to thepolyester was provided to each sheath hole of the spinning holes. Andthe melt spinning was carried out on the conditions with 280° C. in aspinning temperature and 3800 m/minute in a spinning speed. Thereafter,spinned filaments were drafted and fined by a suction device. The spunfilaments discharged from the suction device were opened. The spunfilaments became to the sheath-core type bicomponent continuous fiberseach of which was 3.3 dtex. And the fibers were accumulated on a movingconveyor and a nonwoven web was formed. The nonwoven web was passedthrough between an embossing roll of which the surface temperature was95° C. and a smooth roll of which the surface temperature was 95° C.Then a total area of convex parts of the embossing roll was 36% per anentire area of the embossing roll. The nonwoven web was partially heatedand pressed on the condition with 294 N/cm in line pressure. As theresult, the nonwoven fabric was obtained and the weight was 50 g/m² .

EXAMPLE 2

The polyethylene-terephthalate which was 0.70 in intrinsic viscosity [η]and 260° C. in melting point was prepared. On the other hand, thepolyethylene which was 21 g/10 minutes in melt flow rate, 0.913 g/cc indensity and 102° C. in melting point was prepared. This polyethylene wasthe mixture of the first polyethylene 60 weight mass and the secondpolyethylene 40 weight mass. The first polyethylene was polymerized bymetallocene catalyst and was 28 g/10 minutes in melt flow rate, 0.906g/cc in density and 97° C. in melting point. The second polyethylene waspolymerized by Ziegler-Natta catalyst and was 14 g/10 minutes in meltflow rate, 0.918 g/cc in density and 106° C. in melting point.

Using the polyester and the polyethylene, the nonwoven fabric wasobtained and the weight was 50 g/m² by the same method of the example 1.

EXAMPLE 3

The polyethylene-terephthalate which was 0.70 in intrinsic viscosity [η]and 260° C. in melting point was prepared. On the other hand, thepolyethylene which was 18 g/10 minutes in melt flow rate, 0.913 g/cc indensity and 104° C. in melting point was prepared. This polyethylene wasthe mixture of the first polyethylene 40 weight mass and the secondpolyethylene 60 weight mass. The first polyethylene was polymerized bymetallocene catalyst and was 28 g/10 minutes in melt flow rate, 0.906g/cc in density and 97° C. in melting point. The second polyethylene waspolymerized by Ziegler-Natta catalyst and was 14 g/10 minutes in meltflow rate, 0.918 g/cc in density and 106° C. in melting point.

Using the polyester and the polyethylene, the nonwoven fabric wasobtained and the weight was 50 g/m² by the same method of the example 1.

EXAMPLE 4

The polyethylene-terephthalate which was 0.70 in intrinsic viscosity [η]and 260° C. in melting point was prepared. On the other hand, thepolyethylene which was 16 g/10 minutes in melt flow rate, 0.910 g/cc indensity and 103° C. in melting point was prepared. This polyethylene wasthe mixture of the first polyethylene 67 weight mass and the secondpolyethylene 33 weight mass. The first polyethylene was polymerized bymetallocene catalyst and was 28 g/10 minutes in melt flow rate, 0.906g/cc in density and 97° C. in melting point. The second polyethylene wasPolymerized by Ziegler-Natta catalyst and was 4 g/10 minutes in meltflow rate, 0.918 g/cc in density and 106° C. in melting point.

Using the polyester and the polyethylene, the nonwoven fabric wasobtained and the weight was 50 g/m² by the same method of the example 1.

EXAMPLE 5

The polyethylene-terephthalate which was 0.70 in intrinsic viscosity [η]and 260° C. in melting point was prepared. On the other hand, thepolyethylene which was 22 g/10 minutes in melt flow rate, 0.909 g/cc indensity and 103° C. in melting point was prepared. This polyethylene wasthe mixture of the first polyethylene 70 weight mass and the secondpolyethylene 30 weight mass. The first polyethylene was polymerized bymetallocene catalyst and was 28 g/10 minutes in melt flow rate, 0.906g/cc in density and 97° C. in melting point. The second polyethylene waspolymerized by Ziegler-Natta catalyst and was 14 g/10 minutes in meltflow rate, 0.918 g/cc in density and 106° C. in melting point.

Using the polyester and the polyethylene, the nonwoven fabric wasobtained and the weight was 50 g/m² by the same method of the example 1.

COMPARATIVE EXAMPLE 1

The polyethylene-terephthalate which was 0.70 in intrinsic viscosity [η]and 260° C. in melting point was prepared. On the other hand, thepolyethylene which was 25 g/10 minutes in melt flow rate, 0.957 g/cc indensity and 130° C. in melting point was prepared. This polyethylene wasa high density polyethylene polymerized by Ziegler-Natta catalyst.

Using the polyester and the high density polyethylene, the nonwovenfabric was obtained and the weight was 50 g/m² by the same method of theexample 1.

Each nonwoven fabric obtained with the examples 1-5 and the comparativeexample 1 was measured or evaluated as the aboves which were describedabout the softness, the soft feeling, the smoothness feeling, thetensile strength and the adhesion strength of each non woven fabric. Andthe result were shown in Table 1. TABLE 1 examples comparative 1 2 3 4 5example 1 the softness (g) 140 160 155 150 170 180 the soft feeling 1 21 1 2 3 the smoothness feeling Bad Mid. Bad Bad Good Bad the tensilestrength (N/5 cm in width) MD direction 205 216 250 217 180 220 CDdirection 108 88 98 95 70 117 the adhesion strength (N) 100° C. 20.620.0 15.7 20.5 15.7 0 110° C. 27.4 22.3 20.3 21.4 20.4 0 130° C. 31.026.1 28.2 30.2 23.5 26.5

Furthermore, FIG. 4 was showing the micrograph of the nonwoven fabricobtained with the example 2. FIG. 5 was showing the micrograph of thenonwoven fabric obtained with the example 3. FIG. 6 was showing themicrograph of the nonwoven fabric obtained with the example 4. FIG. 7was showing the micrograph of the nonwoven fabric obtained the example5.

In the nonwoven fabrics obtained with the examples 1-5, each of thecontinuous fibers had irregular unevenness on the each surface along theaxial direction and circular direction of the fiber. On the other hand,in the nonwoven fabrics obtained with the comparative example 1, each ofthe continuous fibers had smooth on the each surface along the axialdirection of the fiber. The each sheath-core type bicomponent continuousfiber obtained with the examples had fine parts and thick parts indiameter by existing the irregular unevenness. Therefore, softness wasgiven to the continuous fiber, as the result, the each of the nonwovenfabrics obtained with the examples 1-5 was softer and had more softfeeling than the nonwoven fabric obtained with the comparativeexamples 1. Because the visible ray was diffusely reflected for theirregular unevenness, the each of the nonwoven fabrics obtained with theexamples 1-5 was more whitish than the nonwoven fabrics obtained withthe comparative examples 1.

Generally speaking, because the first polyethylene polymerizedmetallocene catalyst had lower melting point, the mixture polyethyleneusing the first polyethylene had too lower melting point. Accordingly,the nonwoven fabrics obtained with the examples 1-5 had higher adhesionstrength than the nonwoven fabric obtained with the comparative examples1, even if the temperature to adhere was low. The configuration of thecross section of the core portion which was made of the polyester didnot change along the axial direction of the fiber as the prior art.Accordingly, the nonwoven fabrics obtained with the examples 1-5 had thesame tensile strength as the nonwoven fabric obtained with thecomparative examples 1 because the core portion had substantially samediameter.

1. A nonwoven fabric containing sheath-core type bicomponent fibers ineach of which: the sheath portion is formed by polyethylene, and thethickness of the sheath portion is changed irregularly and at randomalong the axial direction and circular direction of the fiber; the coreportion is formed by polyester, and the configuration of the coreportion is not substantially changed along the axial direction of thefiber.
 2. The nonwoven fabric according to claim 1 wherein thesheath-core type bicomponent fiber is continuous.
 3. The nonwoven fabricaccording to claim 1 wherein the polyethylene is the mixture of thefirst polyethylene polymerized by metallocene catalyst and the secondpolyethylene polymerized by Ziegler-Natta catalyst.
 4. The nonwovenfabric according to claim 3 wherein the second polyethylene is lowdensity polyethylene.
 5. The sheath-core type bicomponent fiber which isprovided into claim
 1. 6. A composite material comprised of the nonwovenfabric of claim 1 and a polyolefin film, which is adhering the nonwovenfabric to the polyolefin film by melting or softening the sheathportion.
 7. A method of the nonwoven fabric comprised of: preparing thepolyester, and the polyethylene mixed the first polyethylene polymerizedby metallocene catalyst and the second polyethylene polymerized byZiegler-Natta catalyst; providing the polyester to each core hole ofsheath-core type spinning holes and the polyethylene to each sheath holeof the sheath-core type spinning holes; accumulating the sheath-coretype bicomponent continuous fibers obtained by melt spinning thepolyester and the polyethylene from the sheath-core type spining holes.8. The method of the nonwoven fabric according to claim 7 wherein themelt flow rate (MFR) of the polyethylene is 16-21 grams per 10 minutes.9. The method of the nonwoven fabric according to claim 7 wherein themelt spinning speed is at a rate of 3000-4000 meters per a minute.